The present invention relates to a vulcanized molded article which comprises an elastomeric polyblend of a thermoplastic copolyester and a vulcanizable synthetic or natural rubber.
Vulcanized natural or synthetic rubbers are widely used for a variety of purposes, such as tubings, hoses, tires, belts, coated fabrics and sealants in the automobile industry. However, such rubbers have various defects and have a restricted usage. For example, SBR (styrene-butadiene rubber) and NR (natural rubber) exhibit poor tensile and tear strength, and poor oil resistance. NBR (nitrile butyl rubber) is comparably superior in oil resistance, but it is sensitive to oxygen or ozone at an elevated temperature. CR (chloroprene rubber) has comparatively good resistance to deterioration caused by heat or oxygen, but they lose their elastomeric properties in certain oils such as ASTM #3 oil or Fuel D. Therefore, there has been needed a rubber having a good elastic property at both low and high temperatures, a good oil resistance, a good abrasion resistance and a good oxygen or ozone resistance.
U.S. Pat. No. 3,965,055 to Shichman et al. discloses a modified elastomer composition of a semi-crystalline, thermoplastic resin and a rubber. However, the resins do not include a polyester of the polybutylene terephthalate series which have been found to be to more advantages.
U.S. Pat. No. 3,963,802 to Shih relates to thermoplastic copolyether esters which are softened with the retention of toughness by blending therewith certain ethylene copolymers.
Furthermore, polyester fibers or fabrics have recently become popular as reinforcing materials because of their excellent rigidity and high modulus and it is strongly desirable to improve the adhesiveness of rubbers to polyesters.
Thus, the principal object of this invention is to provide a vulcanized elastomeric compound having good resilience at low and high temperatures, heat and oxygen/ozone resistance, excellent oil and fuel resistance, impact strength, good abrasion property and increased scuff resistance. In addition, the blends which are rich in copolyester exhibit superior ozone resistance, oil and fuel resistance, improved stiffness, impact resistance and electric insulating properties and their mechanical strength are maintained even at elevated temperatures.
Another object of this invention is to provide a rubber composition having a good adhesive strength to polyester fibers or fabrics.
We have found the foregoing objects are achieved by blending a thermoplastic copolyester with a synthetic or natural rubber and vulcanizing the polyblend. It is a surprising discovery that copolyester or copolyester elastomers are so compatible with rubber that an intimate blend is achieved.